The invention relates to a method for deforming a hollow workpiece having at least one open end, wherein the workpiece is clamped down in a clamping device, at least one forming tool is placed into contact with a wall of the workpiece, the workpiece and said forming tool are rotated about an axis relative to each other and the workpiece is deformed by means of the forming tool. The invention furthermore relates to a forming machine in accordance with the preamble of claim 9, by means of which a hollow workpiece having at least one open end can be deformed, and to a catalytic converter unit for a vehicle.
Such a method and forming machine are known, e.g. from European patent application EP 0 916 428. Said patent application discloses a forming machine comprising a forming head including a number of rollers, by means of which the diameter of one end of a circular cylindrical metal element is reduced, and in addition said end is bent through an angle.
To this end, the metal cylinder is clamped down and the forming head is rotated about an axis of rotation, after which said end is deformed by pressing the rollers in radial direction (relative to said axis of rotation) against the outer of the metal cylinder and moving them along said outer side in a number of cycles whilst decreasing the radial distance between the rollers and the axis of rotation with each cycle, as a result of which a reduction of the diameter is obtained. Since the axis of rotation extends at an angle to the central axis of the metal cylinder, the end of the cylinder is not only reduced as a result of the movement in radial direction of the rollers, but in addition said end will moreover be positioned at an angle. Due to the use of the aforesaid cycles, the workpiece assumes the shape of the final product in steps.
EP 0 916 426 discloses a comparable method and forming machine, in which the axis of rotation is eccentrically offset from the central axis of the metal cylinder. In this way a product is obtained wherein the central axis of the deformed part is likewise offset from the central axis of the non-deformed part of the metal cylinder.
The present method and apparatus can e.g. be used in the production of the housings of catalytic converters that form part of the exhaust system of vehicles, such as cars. The diameter of such catalytic converters is larger than the diameter of the pipes of the exhaust system of which they form part, and they are preferably positioned close to the engine block in order to reach their operating temperature as quickly as possible after the engine has been started, and in order to maintain that temperature as well as possible. A first consequence of this is that the diameter of the connections on either side of the catalytic converter housing must be reduced, in order to achieve a proper connection with the rest of the exhaust system, whilst furthermore said connections often need to have a complicated shape in order to be able to position them optimally with respect to the engine block.
The aforesaid known methods and forming machines for manufacturing workpieces having at least one deformed end only allow circular operations, which is inadequate, considering the increasingly complex shapes that designers require.